1. Field of the Invention
The present invention relates to an inductor, and more particularly, to an inductor structure made with integrated circuit technology.
2. Description of the Prior Art
An inductor is a passive electronic component that stores energy in the form of a magnetic field, and an inductor tends to resist any change in the amount of current flowing through it. The inductor is usually used with capacitors in various wireless communications applications for providing stable currents, switched phases, filtering and resonance. In its simplest form, the inductor consists of a wire loop or coil. The inductance is directly proportional to the number of turns, the thickness, the length, and the radius of the coil. The inductance also depends on the type of material around which the coil is wound. In a semiconductor manufacturing process, at least two metal layers with specifically designed layout patterns and a plurality of via plugs for connecting these two metal layers are used to form a wire loop, thus fabricating an inductor onto an integrated circuit chip. Recently, for obtaining an inductor with a smaller size, a three-dimensional inductor is produced to have an increased coil density.
Please refer to FIG. 1 showing a conventional schematic diagram of two-level spiral inductor 10. For saving chip area, as shown in FIG. 1, the inductor 10 is designed as two layered coils. The inductor 10 has two ends P1 and P2 and spirally circles a point C starting at the outer end P1 from an outer ring to an inner ring for a desired number of loops, which is then connected to another layer by a via plug, and spirals from an inner ring to an outer ring finally connecting to the end P2. It deserves to be mentioned that current flowing in the two layered coils is in the same direction which increases the mutual inductance of the inductor 10, that is, the current flows into the end P1 from the outer ring to the inner ring in a clockwise direction then connects to the second layer by the via plug, and similarly flows clockwise from the inner ring to the outer ring to the end P2.
Please refer to FIG. 2 showing a turn with essential components in a three-dimensional inductor manufactured using a conventional semiconductor technology disclosed in U.S. Pat. No. 6,037,649. The three-dimensional inductor 20 is made on a substrate 21 and comprises an N-turn coil. Each turn comprises a first-level metal line (M1) having a first end and a second end, a second-level metal line (M2) having a first part and a second part, and a third-level metal line (M3) having a first end and a second end which are isolated through the first, the second, and the third isolating layers. The adjacent levels of metal lines may be connected through the via plugs (24 and 27) in the isolating layers. The integral coil of the three-dimensional inductor is accomplished and extends along the direction of the magnetic field of the three-dimension inductor by connecting the second-level metal line (M2) in the Nth turn with the third-level metal line (M3) in the (N+1)th turn coil.
The inductor structures described above include only one inductor structure in the entire structure space. Therefore, the research and development to improve the integration level for an inductor structure is still needed.